An air pressurized ski boot is known from the German Offenlegungsschrift No. 2 316 014, where a pump-pressure valve enters a membrane-pump chamber and is actuated externally through a flap present in the wall of the membrane pump chamber to vent the inflatable air chamber. Accordingly, the membrane pump chamber may be actuated only from outside the region provided for the pump pressure valve when pumping is in progress and hence proper actuation will not necessarily be assured. Moreover, the assembly of the pump pressure valve to the membrane pump chamber and to the shoe is complex, and so also is the assembly of the entire pumping system to the shoe.
German Offenlegungsschrift No. 33 10 812 discloses a pump system to inflate an air chamber inside a ski boot where the pump pressure valve is mounted in the wall of the membrane pump chamber. Screwing tight a closure element will seal the flow path from the pump chamber to the air chamber. This closure element is mounted next to the pump chamber and is provided with a manually actuated venting valve allowing the evacuation of the air chamber when the closure element is shut. This pump system is relatively complex and, furthermore, not particularly convenient because the closure element must first be screwed in or out when a user is inflating or evacuating the air chamber.